158 SEN5IBLE PERSPIRATION. 



The nature of the liquor perspired has been 

 already noticed, p. 68. In hot weather it 

 has been observed by Hales, Du Hamel and 

 Guettard to partake occasionally of the pe- 

 culiar scent of the plant that yields it, but in 

 general the odorous matter is of too oily a 

 nature to be combined with it. 



The sensible perspiration of plants is of 

 various kinds. When watery, it can be con- 

 sidered only as a condensation of their in- 

 sensible evaporation, perhaps from some sud- 

 den change in the atmosphere. Groves of 

 Poplar or Willow exhibit this phenomenon, 

 even in England, in hot calm weather, when 

 drops of clear water trickle from their leaves 

 like a slight shower of rain. Sometimes it is 

 of a saccharine nature, as De la Hire ob- 

 served in Orange trees ; Du Hamel Arb. 

 v. 1. 150. It is more glutinous in the Tilia 

 or Lime-tree, more resinous in Poplars, as 

 well as in Cistus creticus, from which last the 

 resin called Labdanum is collected, by beat- 

 ing the shrub with leather thongs. See 

 Tournefort's Voyage, 29. In the Fraxinella, 

 Dictamnm albas, it is a highly inflammable 

 vapour. Ovid has made an elegant use of the 

 4 



